In a normal power generator installed in a motor vehicle, when a field winding of the power generator is intermittently energized by a voltage regulator while a rotor of the power generator is rotated by rotational power supplied from the internal combustion engine (engine) of the motor vehicle, the rotating field winding creates magnetic flux. The created magnetic flux magnetizes a plurality of field poles of the rotor. The rotation of the plurality of magnetized field poles creates magnetic flux, and the created magnetic flux induces a multiphase AC voltage in multiphase armature windings. The multiphase AC voltage induced in the multiphase armature windings is rectified by a rectifier, so that a direct current (DC) voltage is generated.
A particular type of such power generators is disclosed in US Patent Application Publication No. 2003/0042809 corresponding to Japanese Patent Application Publication No. 2003-79198. A three-phase alternator disclosed in the Patent Publication is configured to compare an AC voltage induced in one phase winding with a threshold voltage level to thereby generate pulses, and start to generate power by starting an excitation current to the field winding when the number of pulses is equal to or higher than a predetermined number.